Micro-pore characteristics and its control factors are analyzed according to mercury penetration, physical property parameters, flake observation and scanning electron microscopy, etc. Studies show that Chang81 reservoir is ultra-low permeability, its main pore types are intergranular pore and feldspar dissolved pore, its main pore throat types are low porosity, fine throat to micro-fine throat. Diagenesis stage of Chang 81 reservoir is situated in the diagenetic stage B. compaction mainly reduce the pore space, while the micro-cracks caused by compaction can be good reservoir space; ferrocalcite cement, Chlorite coating and kaolinite would destroy the reservoir space by filling in the primary pores and secondary pores; hydration of feldspar would destroy the reservoir space, while dissolution of feldspar would improve the reservoir space; dissolution of feldspar is the most favorable diagenesis.

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